In the process of manufacturing printed circuit boards, UV curable photoresist are used. The exposed portion of the photoresist becomes insoluble in developer solution (dilute alkaline solution) and forms a protective barrier to other processing chemicals (for example, etching and plating solutions). The unexposed portion of the photoresist needs to rinse freely from the circuit board with a mild alkaline solution (for example, 1% sodium carbonate, monohydrate in water). The development occurs because the polymer in the photoresist contains acid functionality. These acid groups within the organic polymer matrix are neutralized in alkaline solution forming a water soluble organic salt. As the dissolved photoresist builds up in solution (called developer loading), insoluble organic materials begin to form in the developing tank, eventually forming a water insoluble scum or residue. The presence of anti-foam additives (conventionally added to developing solutions to minimize foaming) greatly increases the tendency for scum to form. As the level of scum builds, chances increase for an inadvertent redeposit of these water insoluble residues onto the developed circuit board. These redeposited residues cause a retardation of the etching solution (etching chemistries have difficulty penetrating any organic residues). Where the etch is retarded, circuit shorts form causing a defective circuit board. In addition to increasing the potential for defective circuit boards, this residue also makes it difficult to clean equipment increasing maintenance time.
Accordingly, it is a primary object of the present invention to provide developing solutions in which the build-up of scum and residue is reduced.